1. Technical Field
The present invention relates to a boom extension and contraction mechanism for a crane apparatus including a boom that is extended and contracted by one hydraulic cylinder.
2. Related Art
Conventionally, there has been known this sort of boom extension and contraction mechanism that includes a boom with a plurality of boom members and one telescopic cylinder; the telescopic cylinder allows the boom to extend and contract by shifting next boom members in front of respective ones with respect to the boom members other than a top boom member; and one of a cylinder rod and a cylinder tube of the telescopic cylinder is connected to the bottom boom member (see, for example, Patent Literature 1).
The boom extension and contraction mechanism includes: a cylinder-to-boom connection mechanism that can connect and disconnect between the other of the cylinder rod and the cylinder tube, and the boom members other than the bottom boom member; and a boom member connection mechanism that can connect and disconnect between the boom members next to one other.
The cylinder-to-boom connection mechanism and the boom member connection mechanism of the boom extension and contraction mechanism are driven by respective hydraulic double acting cylinders. Therefore, two hydraulic hoses to supply and discharge hydraulic oil are required for each of the hydraulic double acting cylinders that drive the cylinder-to-boom connection mechanism and the boom member connection mechanism, respectively. The double acting cylinders are provided in the other of the cylinder rod and the cylinder tube of the telescopic cylinder, and therefore change in their positions according to the telescopic motion of the telescopic cylinder. The hydraulic hose connected to each of the double acting cylinders is wound around a hose reel provided on a swivel base to which the base end of the boom is connected, and therefore is reeled out and off according to the telescopic motion of the boom. In addition, the hydraulic hose connected to each of the double acting cylinders is a twin hose having a pair of hydraulic oil passages integrally formed with each of the double acting cylinders.
The boom extension and contraction mechanism further includes a boom detection sensor that detects which of the boom members is connected to the telescopic cylinder. Therefore, a communication cable is required to transmit a detection signal from the boom detection sensor. The boom detection sensor is provided in the other of the cylinder rod and the cylinder tube of the telescopic cylinder, and therefore changes in its position with respect to the base end of the boom according to the telescopic motion of the telescopic cylinder. Therefore, the communication cable wound around a cord reel provided on the swivel base like the hose reel is reeled out and off according to the telescopic motion of the boom.
This boom extension and contraction mechanism needs two hose reels around which the pair of hydraulic hoses is wound, and also needs a cord reel around which the communication cable is wound. As a result, the number of parts is increased and the structure of the based end of the boom is complicated.
Moreover, the twin hose is normally wound around the hose reel outward in the radial direction in order to make the fleet angle a predetermined angle or lower in terms of the relationship with the sheave that guides the twin hose. Therefore, the hose reel around which the twin hose is wound is increased in size in the radial direction. Consequently, when mounted on the swivel base, the hose reel substantially protrudes backward from the swivel base. As a result, the counter weight mounted on the back of the swivel base protrudes further to increase the angle of traverse, and therefore the working efficiency may be deteriorated.
To solve this problem with an increase in the angle of traverse of the counter weight, a boom extension and contraction mechanism is expected which includes the cylinder-to-boom connection mechanism and the boom member connection mechanism driven by hydraulic single acting cylinders, respectively, and also includes a hydraulic oil passage to supply hydraulic oil to each of the single acting cylinders, which is provided in each of the cylinder tube and the cylinder rod of the telescopic cylinder. With this boom extension and contraction mechanism, the hydraulic oil passage to supply hydraulic oil to each of the single acting cylinders extends and contracts according to the telescopic motion of the telescopic cylinder. Therefore, merely the inlet/outlet of the hydraulic oil passage provided in the telescopic cylinder is connected to each of the single acting cylinders, so that a hose reel is not needed.
Patent literature 1: Japanese Patent Application Laid-Open No. 2002-332194
Here, with the boom extension and contraction mechanism without a hose reel, it is possible to reduce the angle of traverse in the back of the swivel base. However, since the hydraulic oil passage is provided in the telescopic cylinder, the structure is complicated, and therefore it is not easy to address a failure that occurs in the telescopic cylinder.